Method and arrangement for detection and destruction of tunnels

ABSTRACT

A method and arrangement for destroying tunnels. A subterraneous, vertical shaft is excavated until a tunnel preventing depth. After liquid is introduced to the shaft, a shaft liner is penetrable by the introduced liquid when a tunnel is present in the vicinity of said shaft, due to the considerably larger pressure of the introduced liquid relative to the bearing capacity of soil interposed between the tunnel and shaft. The tunnel is then flooded and destroyed following passage of the liquid through the liner. A system for detecting and destroying tunnels in the proximity of a security-sensitive facility comprises a hollow member anchored to the upper soil surface adjoining each shaft, a sensor having a unique address mounted on a corresponding hollow member for generating an electrical output when the liquid level has been reduced more than a predetermined level, and a computer in data communication with each of the sensors.

FIELD OF THE INVENTION

The present invention relates to the field of detection equipment. More particularly, the invention relates to a method and arrangement for detecting tunnels.

BACKGROUND OF THE INVENTION

Due to the increasing number of worldwide terrorist activities, terrorists have become more daring and imaginative in terms of the way that they perpetrate their malicious schemes. Many terrorists have recently dug tunnels underneath military posts, through which arms, weapons, and even heavy machinery are smuggled without being noticed by security personnel. By digging tunnels in a carefully planned fashion and passing through the tunnels, some terrorists succeed in infiltrating security-sensitive facilities such as military posts, jails, airports, nuclear power plants and international borders.

Many methods are known for locating tunnels, such as by magnetic, optic and ultrasonic means. However, none of these methods are capable of both detecting and destroying tunnels simultaneously. A need therefore exists for detecting and destroying tunnels simultaneously.

It is an object of the present invention to provide a method and arrangement for simultaneous detection and destruction of newly dug tunnels.

It is an additional object of the present invention to provide a method and arrangement for the automatic destruction of newly dug tunnels prior to human detection thereof.

Other objects and advantages of the invention will become apparent as the description proceeds.

SUMMARY OF THE INVENTION

The present invention provides a method for destroying tunnels, comprising excavating a subterraneous, substantially vertical shaft until a tunnel preventing depth; applying a liner onto, or adjacent to, the inner wall/walls of said shaft; introducing liquid to said shaft until said shaft is substantially filled; and allowing said liquid to burst said liner when a tunnel is present in the vicinity of said shaft, due to the considerably larger pressure of said introduced liquid relative to the bearing capacity of soil interposed between the tunnel and shaft, thereby flooding and destroying the tunnel.

As referred to herein, the “tunnel preventing depth” to which a shaft is excavated means a depth underneath an upper soil surface which will not support the digging of a tunnel due to the low bearing capacity of the soil, e.g. gravel, at said depth, due to the existence of groundwater at said depth, or due to the relatively high labor-intensive or time-consuming process which is needed for the removal of soil constituents at that depth, such as a solid ledge of hard rock, e.g. granite, or of hardpan at a depth of e.g. 50 m.

For most types of soil adjoining the tunnel, the liner is a sealing element or polymeric material.

When the soil adjoining the tunnel is sand, the liner is a flexible hollow element, such as rubber, having an open proximal end, i.e. the end closer to the upper soil surface, and a closed distal end, i.e. the end more distant from the upper soil surface. The liner is applied adjacent to the wall/walls of the shaft by: placing the liner at the proximal end of the shaft; introducing liquid to the shaft while the proximal end of said liner is retained until the shaft is substantially filled, whereby the liner expands substantially to the inner wall/walls of the shaft after liquid is introduced into the shaft; and anchoring the proximal end of said liner.

As referred to herein, a liner is “anchored” when its proximal end is fixedly attached to the upper soil surface. Typical anchoring means include stakes, plaster, concrete, stones, packed sand, and the like.

Preferably, the introduced liquid is water.

In a preferred embodiment of the invention, a tunnel is detected by sensing a reduced depth of liquid in the shaft.

In one aspect, the depth of liquid in the shaft is sensed by anchoring a hollow member, together with the proximal end of the liner, if a hollow liner is employed, to the proximal end of the shaft; and deploying sensing equipment in contact with said hollow member.

In one aspect, the depth of liquid in the shaft is sensed visually. A float provided. with an upwardly extending rod is placed on the upper layer of the introduced liquid; and a tunnel is detected by visually sensing a reduced protrusion of the rod from the upper soil surface. When a plurality of shafts are employed, the protrusion of each corresponding rod from the upper soil surface is compared.

In one aspect, the depth of liquid in the shaft is sensed by a sensor. The sensor is selected from the group of limit switch, interphase sensor, and capacitive transduction sensor.

Following the destruction of a tunnel in the, vicinity of a shaft by the liquid bursting the liner of the shaft and flooding the tunnel, the soil interposed between the flooded tunnel and shaft is in a collapsed configuration. After the presence of said tunnel is detected, as indicated by a reduced depth of liquid in the shaft, the shaft is preferably filled with tunnel preventing material, such as concrete.

The present invention is also directed to an arrangement for destroying tunnels, comprising: a subterraneous, substantially vertical shaft; and a liner applied onto, or adjacent to, the inner wall/walls of said shaft, said liner adapted for retaining liquid introduced into said shaft, wherein said liner is penetrable by said introduced liquid when a tunnel is present in the vicinity of said shaft, due to the considerably larger pressure of said introduced liquid relative to the bearing capacity of soil interposed between the tunnel and shaft, the tunnel being flooded and destroyed following passage of said liquid through said liner.

In one aspect, the liner is a flexible hollow element having an open proximal end and a closed distal end, said proximal end being anchored to an upper soil surface and said liner being expandable within the shaft, upon the introduction of a liquid therewithin.

In a preferred embodiment of the invention, the arrangement further comprises means for detecting the presence of a tunnel.

The means for detecting the presence of a tunnel preferably comprises a sensor for sensing a reduced depth of liquid within the shaft.

In one aspect, the arrangement further comprises a hollow member which is anchored, together with the proximal end of the liner, to the upper soil surface, equipment associated with a sensor being in contact with said hollow member.

In one aspect, the sensor is a float provided with an upwardly extending rod which is placed on the upper layer of the introduced liquid, a tunnel being detected by visually sensing a reduced protrusion of the rod from the upper soil surface. The shaft is preferably covered by a cover provided with a tube downwardly extending from the underside thereof, for encircling the rod and retaining it in a substantially upright position.

In one aspect, the sensor is mounted on the hollow member. The sensor is selected from the group of limit switch, interphase sensor, and capacitive transduction sensor.

The present invention is also directed to a system for detecting and destroying tunnels in the proximity of a security-sensitive facility, comprising:

-   -   a) a plurality of subterraneous, substantially vertical shafts         excavated in the proximity of a security-sensitive facility,         such as military posts, jails, airports, nuclear power plants         and international borders;     -   b) a liner applied onto, or adjacent to, the inner wall/walls of         each of said shafts, for retaining liquid introduced into the         corresponding shaft, wherein each of said liners is penetrable         by said introduced liquid when a tunnel is present in the         vicinity of the corresponding shaft, due to the considerably         larger pressure of said introduced liquid relative to the         bearing capacity of soil interposed between the tunnel and said         shaft, the tunnel being flooded and destroyed following passage         of said liquid through said liner;     -   c) a hollow member insertable within, and anchored to the upper         soil surface adjoining, each shaft;     -   d) a sensor mounted on the hollow member of each shaft for         sensing a reduced depth of liquid within the corresponding shaft         and generating an electrical output when the liquid level has         been reduced more than a predetermined level, each sensor being         assigned a unique address; and     -   e) a computer in data communication with each of the sensors,         for displaying the address of each sensor that generated an         electrical output.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a schematic drawing of an arrangement according to one embodiment of the invention, showing a shaft filled with a liquid to a first level;

FIG. 2 is a schematic drawing of the arrangement of FIG. 1, showing the egress of liquid from the shaft when a tunnel is detected in the presence thereof and the liquid level is reduced to a second level;

FIG. 3 is a schematic plan view of a plurality of shafts excavated along one row; and

FIG. 4 is a schematic plan view of a plurality of shafts excavated in offset formation.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 illustrates an arrangement for detecting and destroying tunnels according to one preferred embodiment of the invention, which is designated by numeral 10. Arrangement 10, which is suitable for destroying tunnels dug in sand, comprises subterraneous, substantially vertical annular shaft 5 which is excavated within soil body 9 to a depth corresponding to approximately the depth of the lowest anticipated level of groundwater 7, flexible tubelike liner 13 having a proximal open end and a closed distal end, e.g. rubber, nylon, or any other suitable thin plastic material having a thickness ranging between 2 microns to 1 mm, and annular member 17, the outer diameter of which is slightly less than the inner diameter of shaft. After annular member 17, which is made of structurally strong material such as fiberglass, polypropylene, plastic or galvanized steel, is inserted within shaft 5 such that it protrudes slightly from upper surface 11 of soil body 9 and the proximal end of liner 13 is interspersed between annular member 17 and soil body 9, the proximal end of liner 13 and the portion of annular member 17 below upper surface 11 of the soil body are anchored to the soil body by means of concrete slab 22.

After liquid, e.g. water, is introduced into shaft 5, liner 13 expands to substantially the inner wall of the shaft. When the upper surface of liquid body 15 which is retained within shaft 5 is at a level of L₁, float 25 connected to upwardly extending rod 27 is placed on the upper surface of liquid body 15. Cover 19 is provided with tube 29, which extends downwardly from the underside thereof and has an outer diameter slightly larger than the thickness of rod 27, is lowered onto annular member 17 such that tube 29 encircles rod 27 and retains the latter in an upright position. The typical pressure of liquid body 15 at a predetermined depth below L₁ is on the order of 10,000 kg/m² at a depth of 10 m.

With reference to FIG. 2, tunnel 39, which is normally horizontally dug, is shown to be at a depth D below upper surface 11 of the soil body. When tunnel 39 attains a characteristic separation distance B from shaft 5, the bearing capacity of soil between tunnel 39 and shaft 5 is reduced to such a degree, due to its reduced thickness, that liner 13 is burst at opening O. Liquid flows at a tremendously high flow rate from shaft 5 to tunnel 39 while permeating the interposed soil I, whereby interposed soil I collapses and tunnel 39 is flooded and destroyed.

It will be appreciated that the flow rate of liquid flowing through burst opening O is a function of many factors, including the type and bearing capacity of soil interposed between the tunnel and shaft, the depth of the tunnel, the diameter of the tunnel, and the pressure of the liquid retained within the shaft at a depth corresponding to the depth of the tunnel. The flow rate of the liquid which bursts forth from opening O is at first relatively low, and then increases exponentially while the size of the opening increases.

Due to the egress of liquid from shaft 5, the level of liquid body 15 is lowered to L₂. Float 25 and rod 27 connected thereto are consequently lowered as well, thereby indicating to an operator that liquid has exited the shaft and that a tunnel is present in the vicinity thereof. An operator generally determines the liquid level within shaft 5 on a regular basis by visually inspecting the height of rod 27 and informs security personnel that a tunnel has been detected. In order to inhibit formation of a new tunnel from the destroyed tunnel, after permeation of liquid through the adjoining soil, security personnel may fill the shaft with tunnel preventing material, such as concrete.

Other sensors (not shown) may be employed as well for detecting the presence of a tunnel in the vicinity of the shaft. One suitable sensor is a limit switch, e.g. a discrete level switch, mounted onto the annular member that is anchored to the upper soil surface adjoining the shaft, and the limit switch is electrically connected to a float and cable. The operator may determine the liquid level contained within the shaft as the float rises and descends within the annular member. The cable is connected to a meter or to an alarm, indicating that the liquid level is at a maximum level, or alternatively, has lowered significantly below the maximum level. The sensor may also be an interphase sensor which monitors the transition between the two phases of liquid and air, indicating to the operator when the liquid level falls below a predetermined level.

The sensor may also be a capacitive transduction sensor, which determines a change in height of the liquid contained within the shaft by measuring the change in the dielectric constant between an outer electrode and inner electrode. Such a sensor is provided with an electrode housing mounted onto the annular member, a liquid column inlet disposed at the bottom of the electrode housing, a measurement circuitry card, and a cable connection. The measurement circuitry card contained within the housing measures the instantaneous capacitance, which is directly proportional to an output voltage. When the output voltage falls below a predetermined threshold, a signal such as an alarm may be generated.

If so desired, depending on the composition of the soil adjoining the shaft, the liner may a sealing element or polymeric material which is applied directly onto the wall or walls of the shaft. The shaft may be circular, square, or any other convenient shape. Similarly, the hollow member, with which a sensor is in contact and which is anchored to the upper soil surface adjoining the shaft, may be circular, square, or any other convenient shape.

As shown in FIGS. 3 and 4, a plurality of shafts may be employed, for tunnel detection in the vicinity of a security-sensitive facility. The plurality of shafts, such as shafts 5A-5D shown in FIG. 3, may be excavated along one row. For example, when the inner- diameter of the shafts range from 80-100 cm, the spacing between adjacent shafts may be 100 cm. Therefore, the maximum, separation from a tunnel to a shaft will not be more than 20 cm, for an average tunnel diameter of 80 cm, thereby resulting in the bursting of the liner in the shaft closest to the tunnel. Alternatively, the plurality of shafts, such as shafts 5E-5H shown in FIG. 4, may be arranged in offset formation. For example, when the inner diameter of shafts range from 80-100 cm, the spacing between adjacent shafts 5E-5F of one row ranges from 28-300 cm, while the spacing between shafts 5E and 5G of two different rows is 200 cm. If a tunnel were detected in the vicinity of a shaft, e.g. shaft 5F, causing liquid to burst forth therefrom, shaft 5F is filled with tunnel preventing material 31, and three additional shafts 5I-5K are excavated in the vicinity of shaft 5F, to prevent a malicious person from continuing the tunnel formation by circumventing shaft 5F. If the malicious person were to reconstruct the tunnel, which is represented by arrow 35, and continue digging in a straight path, he would encounter shaft 5F which is filled with tunnel preventing material. If he were interested in the time-consuming process of removing the tunnel preventing material in order to continue the previous direction of the tunnel, the malicious person would approach shaft 5J and the tunnel would be destroyed and flooded by the liquid bursting therefrom. If the malicious person decided to change the direction of the tunnel, as represented by arrow 36, the tunnel would be destroyed and flooded by the liquid bursting from shaft 51 when the end of the tunnel is separated from shaft 51 by a distance less than the characteristic separation B (FIG. 2) which causes the corresponding liner to burst.

An array of shafts provided with liners in accordance with the present invention on the order of a hundred or even a thousand shafts may be employed to detect the presence of a tunnel in the proximity of a security-sensitive facility such as military posts, jails, airports, nuclear power plants and international borders. A sensor which generates an electrical output is associated with each shaft and is assigned a unique address. The electrical output of each sensor is in data communication with a computer at a control center. When the liquid level contained within a shaft is lowered more than a predetermined value, indicating the presence of a tunnel in the vicinity of that shaft, the address of the sensor which generated the warning signal is displayed. Security personnel are then dispatched to the vicinity of the shaft, corresponding to the displayed sensor address, whereupon the shaft having the reduced liquid level is filled with tunnel preventing material.

While some embodiments of the invention have been described by way of illustration, it will be apparent that the invention can be carried into practice with many modifications, variations and adaptations, and with the use of numerous equivalents or alternative solutions that are within the scope of persons skilled in the art, without departing from the spirit of the invention or exceeding the scope of the claims. 

1. A method for destroying tunnels, comprising: a) excavating a subterraneous, substantially vertical shaft until a tunnel preventing depth; b) applying a liner onto, or adjacent to, the inner wall/walls of said shaft; c) introducing liquid to said shaft until said shaft is substantially filled; and d) allowing said liquid to burst said liner when a tunnel is present in the vicinity of said shaft, due to the considerably larger pressure of said introduced liquid relative to the bearing capacity of soil interposed between the tunnel and shaft, thereby flooding and destroying the tunnel.
 2. The method according to claim 1, wherein the liner is a sealing element.
 3. The method according to claim 1, wherein the liner is polymeric material.
 4. The method according to claim 1, wherein the liner is a flexible hollow element having an open proximal end and a closed distal end.
 5. The method according to claim 4, wherein the liner is applied adjacent to the wall/walls of the shaft by: a) placing the liner at the proximal end of the shaft; b) introducing liquid to the shaft while the proximal end of said liner is retained until the shaft is substantially filled, whereby the liner expands substantially to the inner wall/walls of the shaft after liquid is introduced into the shaft; and c) anchoring the proximal end of said liner.
 6. The method according to claim 4, wherein the liner is rubber.
 7. The method according to claim 1, wherein the introduced liquid is water.
 8. The method according to claim 1, further comprising the step of detecting a tunnel by sensing a reduced depth of liquid in the shaft.
 9. The method according to claim 8, wherein the depth of liquid in the shaft is sensed by anchoring a hollow member to the proximal end of the shaft; and deploying sensing equipment in contact with said hollow member.
 10. The method according to claim 9, wherein the depth of liquid in the shaft is sensed visually.
 11. The method according to claim 10, wherein a float provided with an upwardly extending rod is placed on the upper layer of the introduced liquid; and a tunnel is detected by visually sensing a reduced protrusion of the rod from the upper soil surface.
 12. The method according to claim 10, wherein the protrusion of each corresponding rod from the upper soil surface is compared, when a plurality of shafts are employed.
 13. The method according to claim 9, wherein the depth of liquid in the shaft is sensed by a sensor.
 14. The method according to claim 13, wherein the sensor is selected from the group of limit switch, interphase sensor, and capacitive transduction sensor.
 15. The method according to claim 8, wherein the shaft is filled with tunnel preventing material after the presence of a tunnel is detected.
 16. An arrangement for destroying tunnels, comprising: a subterraneous, substantially vertical shaft; and a liner applied onto, or adjacent to, the inner wall/walls of said shaft, said liner adapted for retaining liquid introduced into said shaft, wherein said liner is penetrable by said introduced liquid when a tunnel is present in the vicinity of said shaft, due to the considerably larger pressure of said introduced liquid relative to the bearing capacity of soil interposed between the tunnel and shaft, the tunnel being flooded and destroyed following passage of said liquid through said liner.
 17. The arrangement according to claim 16, wherein the liner is a flexible hollow element having an open proximal end and a closed distal end, said proximal end being anchored to an upper soil surface and said liner being expandable within the shaft upon the introduction of a liquid therewithin.
 18. The arrangement according to claim 16, further comprising means for detecting the presence of a tunnel.
 19. The arrangement according to claim 18, wherein the means for detecting the presence of a tunnel comprises a sensor for sensing a reduced depth of liquid within the shaft.
 20. The arrangement according to claim 19, further comprising a hollow member which is anchored to the upper soil surface, equipment associated with a sensor being in contact with said hollow member.
 21. The arrangement according to claim 20, wherein the sensor is a float provided, with an upwardly extending rod which is placed on the upper layer of the introduced liquid, a tunnel being detected by visually sensing a reduced protrusion of the rod from the upper soil surface.
 22. The arrangement according to claim 21, wherein the shaft is covered by a cover provided with a tube downwardly extending from the underside thereof, for encircling the rod and retaining it in a substantially upright position.
 23. The arrangement according to claim 20, wherein the sensor is mounted on the hollow member.
 24. The arrangement according to claim 23, wherein the sensor is selected from the group of limit switch, interphase sensor, and capacitive transduction sensor.
 25. A system for detecting and destroying tunnels in the proximity of a security-sensitive facility, comprising: a) a plurality of subterraneous, substantially vertical shafts excavated in the proximity of a security-sensitive facility; b) a liner applied onto, or adjacent to, the inner wall/walls of each of said shafts, for retaining liquid introduced into the corresponding shaft, wherein each of said liners is penetrable by said introduced liquid when a tunnel is present in the vicinity of the corresponding shaft, due to the considerably larger pressure of said introduced liquid relative to the bearing capacity of soil interposed between the tunnel and said shaft, the tunnel being flooded and destroyed following passage of said liquid through said liner; c) a hollow member insertable within, and anchored to the upper soil surface adjoining, each shaft; d) a sensor mounted on the hollow member of each shaft for sensing a reduced depth of liquid within the corresponding shaft and generating an electrical output when the liquid level has been reduced more than a predetermined level, each sensor being assigned a unique address; and e) a computer in data communication with each of the sensors, for displaying the address of each sensor that generated an electrical output. 